The present invention generally relates to sensor methods and systems. The present invention specifically relates to sensor methods and systems for detecting chemical agents and gases. The present invention also relates to humidity sensors. Additionally, the present invention relates to polymer humidity sensors and sensor substrates thereof.
A variety of sensors for detecting chemical agents and gases have been developed. A basic chemical detecting sensor well known in the art is a humidity sensor. In general, a humidity sensor measures the humidity level by measuring the change in the resistance of an element or the change in the electrostatic capacity of that element as it absorbs or releases moisture. Such sensors can also be utilized for detecting chemicals and gases, in addition to merely the level humidity available in a given environment
Generally, humidity sensors can be classified as belonging to either one of two classesxe2x80x94a resistance type (or resistance-variation type) humidity sensor and a capacitance type (or capacitance-variation type) humidity sensor. A resistance type humidity sensor detects relative humidity by measuring the change in the resistance of an element corresponding to the ambient humidity. In comparison, a capacitance type humidity sensor detects humidity by measuring the change in the electrostatic capacity of an element corresponding to the ambient humidity. The capacitance type humidity sensors typically do not exhibit a satisfactory linear relationship between the capacitance and humidity, and an external circuit is required to overcome this disadvantage. This increases the manufacturing cost of capacitance-change type humidity sensors. Thus, the resistance type humidity sensors, which generally exhibit a linear relationship between the resistance and humidity, appear to have been the preferred choice.
Most of the resistance type humidity sensors include an electrolytic, polymeric, or metallic oxide sensor element. An electrolytic sensor element, which has become the most predominant type of humidity sensors, can be constructed by forming a layer of moisture-lyzable (i.e., hydrolyzed by moisture) electrolyte on an insulating moisture-absorbing substrate. Polymeric films have been used as a humidity-sensing element. Polymer-based humidity-sensing elements can generally be classified into two categories: capacitance-type and impedance-type. The former typically involves more complicated circuit design and manufacturing process, and thus is more expensive, than the latter. An impedance-type electric humidity-sensing element changes its electrical impedance as the humidity of the surrounding environment changes, and the measured impedance is converted into humidity readings. The polymer-based sensing elements can also be further classified into two categories: porous (or more specifically, micro-porous) type, and non-porous type.
The problem of developing small, real time point detection systems for chemical agents is being addressed by laboratories and research facilities in the United States and throughout the world. These laboratories and research facilities have attacked the problem by developing various detection schemes, but virtually all utilize the same substrate to build their sensing device: a silicon or alumina platform with deposited gold or platinum wiring. This substrate introduces special problems to the sensor design. Silica substrates with gold wiring are expensive and sometimes need to be post-processed at the manufacturing facility. Both silica and alumina substrates have shown polymer adhesion problems, which presents difficulties in polymer based humidity sensors, particularly those adapted for use in detecting chemical agents. Alumina is also a relatively good thermal conductor, which can lead to sensor film breakdown. Silica is brittle and alumina is rigid. While cost issues and fabrication problems can be overcome in a laboratory or research environment, this is not true in current commercial manufacturing facilities.
Based on the foregoing, the present inventors have concluded that an alternative substrate for a sensing device must be developed in order to increase the efficiency and deployment of sensing devices used to detect chemical agents and gases, including humidity-types sensors. A stable and reliable substrate foundation is an important factor in sensor efficiency. Important factors in implementing a sensor include the accuracy, interchangeability, long-term stability, resistance to chemical and physical contaminants, along with size and cost effectiveness. Such factors can be addressed through the development of an improved sensor substrate. The present inventors have conducted research and experiments aimed at addressing this substrate issue. As a result of this research and experimentation, the present inventors believe that a polymer presents a good candidate for an ideal sensor substrate. The use of a polymer as a sensor substrate is described in greater detail herein.
The following summary of the invention is provided to facilitate an understanding of some of the innovative features unique to the present invention and is not intended to be a full description. A full appreciation of the various aspects of the invention can be gained by taking the entire specification, claims, drawings, and abstract as a whole.
It is, therefore, one aspect of the present invention to provide improved sensor methods and systems.
It is yet another aspect of the present invention to provide an improved sensor for detecting chemical agents and gases.
It is also an aspect of the present invention to provide an improved humidity sensor.
It is yet another aspect of the present invention to provide an improved substrate upon which sensors for detecting chemical agents and gases can be formed.
It is still another aspect of the present invention to provide a polymer as an ideal sensor substrate.
The above and other aspects can be achieved as is now described. A sensing device formed upon a substrate, including a method of forming the sensing device, is disclosed herein. A substrate can be provided, which is formed from a polymer. A sensor circuit can then be patterned and formed upon the substrate. One or more carbonized filaments can also be formed upon the substrate for use with the sensor circuit. The sensor circuit itself can comprise a capacitive type sensor circuit. A polymer can be coated over the sensor circuit and circuit components thereof to form an all polymer sensor for use in detecting chemical agents. Such a polymer can comprise, for example, HMPTAC (2-hydroxy-3-methacryloxypropyl trimethylammonium chloride). The all polymer sensor formed thereof can also be utilized as a humidity sensor. The polymer can be laser carbonized by an argon ion laser to form the plurality of carbonized filaments. The polymer itself can comprise KAPTON(copyright).